,/ 



The Nautilus. 



Vol. VI. DECEMBER, 1892. No. 8 



PRELIMINARY DESCRIPTIONS OF NEW MOLLTJSCAN FORMS FROM 

 WEST AMERICAN REGIONS, ETC. 



BY ROBERT E. C. STEARXS, U. S. NATIONAL MUSEUM. 



Tlvanilla regina Stearns. 



Shell conical, imperforate, black or purplish-black ; whorls six to 

 seven, concave, longitudinally somewhat obliquely plicated, the 

 plicie more or less projecting at the suture, and on the edge of the 

 basal whorl, producing an undulating or crenulated effect. Other- 

 wise sculptured by incremental strise which traverse the surface and 

 cross the plicre at right angles. Base concave, radiately, closely and 

 prominently striated, more conspicuous, flattened, coalescing, and 

 sinuously curving at the edge. Commencing at the point where the 

 outer lip joins the body whorl, a shallow groove follows parallel to 

 the periphery and extends toward the aperture, without interrupting 

 the basal sculpture. Aperture obliquely subangulate, black-rimmed 

 and crenulated on the thin edge of the outer lip ; nacreous, silvery 

 white toward the edge, bright lustrous golden yellow within and 

 around the umbilical region which latter though deeply pitted is not 

 open. Columella white, calloused, arcuated with a moderately 

 developed rib bounding the umbilical depression, and terminating 

 in a single tubercle. This rib is paralleled by a shallow furrow 

 terminating in a notch just below the tubercle, and by an exterior 

 or outer ridge, part of the way double, of a brilliant orange color ; 

 this orange-colored rib is also exteriorly bounded by a shallow 



